When it’s time to replace your old furnace, the salesman may offer you a newer, more efficient model that has a higher BTU per hour than your old one. What’s more important than the BTUs is the output capacity. Here are some numbers to put it in context: input: 60,000 BTU/hr. (old) vs. 69,000 BTU/hr. (new) = 15% increase. Output: 48,000 BTU/hr. (old) vs. 65,550 BTU/hr. (new) = 37% increase. This is important if you have a well-insulated home. You won’t feel much difference until it turns on, then it will feel like a blast from the desert. If you have a home that’s not well-insulated, you will get intermittent blasts of heat while still feeling the cold from the windows and walls.
Read the full article here: How Replacing A Furnace Can Make You Less Comfortable GreenBuildingAdvisor.com